The recent enhancement of the resolution of the semiconductor device manufacturing process is accompanied by significant influences of film thickness variations. One known cause of film thickness variations is the nature of the CMP (chemical mechanical polishing) process, such as the polishing time and the polishing pressure. Another known cause is an uneven surface structure against which a film deposition or a CMP process is to be performed, due to multiple structure components with different gate dielectric thicknesses placed in the same shot. Still another known cause of film thickness variations is an influence of dishing and erosion, which may occur depending on the layout pattern density.
One known technique for reducing film thickness variations is to place CMP dummy patterns over the wafer. As to CMP dummy pattern placement, the following two techniques are known: A first known technique is to place dummy patterns depending on the data ratios of respective regions in each shot. A second known technique is to place dummy patterns in the peripheral region of the wafer. These techniques aim at improving the flatness of the wafer surface by making the CMP pressure uniform over the wafer with dummy patterns of the same height.
In the above-described techniques, however, surface irregularity generated by film deposition of an oxide film or the like is not taken into account. In a region in which multiple structure components with different heights are placed, surface irregularity is generated depending on the heights and density of the structure components; however, the above-described techniques do not address this issue.
In connection with the above, Japanese Patent Application Publication No. 2002-198419A discloses a manufacturing and designing method of semiconductor devices. In the technique disclosed in this patent document, a film to be processed with a CMP process is formed to cover a semiconductor substrate in which dummy patterns separated by trench isolations are placed in isolation regions. This is followed by planarization with the CMP process. This technique effectively reduces dishing and erosion and achieves improved surface flatness. In this technique, the planar sizes of the dummy patterns and the widths of the trenches are determined on the basis of the ratio of the sum of the planar sizes of the protruding portions of the film to be processed with the CMP process to the overall area size in the peripheral region (the occupation density of the film to be processed with the CMP process in the peripheral region).